Study: Oral HIV infections may be more easily transmitted than previously thought

Researchers at the University of Texas Southwestern Medical Center in Dallas have used an animal model to track how HIV may enter the body following oral exposure to the virus, and they conclude that oral HIV infections may be more easily transmitted than previously thought. In a study published in the December 3 edition of the journal AIDS, the researchers report tracking which tissues in the mouth and digestive tract of rhesus monkeys were first infected with the simian version of HIV when the virus was placed against the inside of the monkeys' cheeks and then swallowed, simulating HIV exposure through either breast milk from HIV-positive mothers to their infants or semen from oral sex. Among the first tissues in which the simian version of HIV could be detected in the monkeys were the soft tissue in the mouth, esophagus, and tonsils, suggesting these sites became infected when initially exposed to the virus. Because the virus likely contacted these tissues when swallowed, the researchers believe HIV-infected milk or semen that enters the mouth and comes in contact with the tissues also could pose an infection risk. At one day after oral exposure and initial infection, lymph nodes near the head and the neck began to show signs of viral infection. Digestive tract tissues below the esophagus did not show signs of HIV infection until four days after oral exposure--the same time as other tissues throughout the body--suggesting that stomach acids likely destroyed the virus when swallowed. "It is clear from our study that the oral and esophageal mucosa and the tonsils are likely to be the most important sites of viral entry," said lead researcher Donald Sodora. "These tissues should be a major focus of any additional studies of HIV or SIV oral transmission." Because SIV spreads so rapidly throughout the bodies of infected monkeys, antiviral therapies can be effective only if they are given within hours of exposure to the virus. Researchers hope the study further identifies one of the major problems facing the formulation of a vaccine: Any vaccine needs to overcome the rapid spread of the virus from the site of infections to tissues throughout the body.